The present invention relates to a mechanical type ultrasonic scanner for mechanically swinging or rotating an ultrasonic vibrator to scan ultrasonic waves.
In such a mechanical type ultrasonic scanner, an ultrasonic vibrator is mechanically swept back and forth, or rotated to transmit ultrasonic waves onto a living organism to be examined, or receive them therefrom, thus obtaining ultrasonic information relating to the organism.
An operating vibrator in a conventional mechanical type ultrasonic scanner cannot be directly brought into contact with the subject to be examined. For this reason, as is shown in FIG. 1, a portion of the mechanical type ultrasonic scanner which is brought into contact with the skin of the patient is covered with plastic or by rubber window member 2. Vibrator 4 is arranged inside window member 2.
With the particular frequency range used to acquire ultrasonic information, it is difficult to transmit an ultrasonic wave if air is present between the vibrator and the skin of the patient. Therefore, liquid (acoustic medium) 6 which allows efficient propagation of the ultrasonic wave is poured into, and fills the space enclosed by window member 2.
In a conventional mechanical type ultrasonic scanner of this type, the rotational motion of a motor (not shown) must be converted into a swinging motion, by use of link mechanism 8 or the like, so as to sweep vibrator 4 back and forth. Unless the motor is completely immersed in liquid 6, liquid 6 will flow out, or bubbles will form between oil seal 11 and shaft 10 directly coupled to the motor. Formation of bubbles in liquid 6 degrades the ultrasonic image. Therefore, the bubbles formed in liquid 6 must be removed by some means or other, and subsequent formation of bubbles must also be retarded.
In the conventional scanner, liquid 6 generates a positive pressure in the space enclosed by window member 2, in order to prevent formation of bubbles or to remove bubbles from liquid 6 itself. In order to pour liquid 6 inside window member 2, a plug must be opened and then closed. The opening and closing of this plug is a rather cumbersome process. In addition, even window member 2 is filled with liquid 6, it is difficult to maintain a sufficiently high positive pressure therein.